1. Field of the Invention
The present invention relates to a sheet feeding device and sheet storage device for use therein, for an image forming apparatus such as a copying machine, printing machine, laser beam printer or the like, and more particularly to an image forming apparatus provided with a box-shaped sheet storage device (hereinafter called "cassette") containing a plurality of sheets.
2. Related Background Art
There is provided therein with a cassette containing a plurality of sheets. As shown in FIGS. 1 and 2, the cassette 1' employed in such image forming apparatus is provided with an inner plate 2' for supporting plural sheets S, and a limiting plate 3 for limiting the lateral movement of said sheets S. Said inner plate 2' is provided with plural elongated holes 4 in the transverse or lateral direction of the sheets, and said limiting plate 3 is so constructed as to be movable in said elongated holes 4 according to the sheet size and to protrude through one of said elongated holes 4. Above the downstream end of said limiting plate 3 there is provided a separating finger 5 for separating the sheets S one by one. At the right side of said inner plate 2' (as seen facing downstream), a side plate 8 is fixed to the bottom plate of the cassette 1', and another separating finger 5 is also provided above the downstream end of said side plate 8. Above said cassette 1' there is rotatably supported a shaft 6 connected to an unrepresented motor and having plural sheet feed rollers 7 corresponding to various sheet sizes. Said inner plate 2' is biased upwards by a spring 9, whereby the sheets S stacked on said inner plate 2' are pressed against the sheet feed rollers 7.
In response to the actuation of an unrepresented start key, the motor is activated to rotate said sheet feed rollers 7, thereby feeding the sheets S. Then, said sheets S are separated one by one by said separating fingers 5 and the uppermost sheet S alone is transported.
However, in a case where narrow sheets S (for example of a width A shown in FIG. 1) are used in the above-explained cassette 1', two sheet feed rollers 7 in the area B may come into direct contact with the inner plate 2', once the number of sheets S on plate 2' has decreased sufficiently, or due to lateral inclination of the inner plate 2' or fluctuation in the precision of the feed rollers 7. Such contact decreases the pressure of the sheet feed rollers 7 in the area A on the sheets S, thus resulting in skewed feeding, overlapped or creases or wrinkles of the sheets S. Also, the rollers 7 in the area B may be abnormally abraded due to friction with the inner plate 2'.
Also in the above-explained conventional image forming apparatus, the cassette 1' may be dropped and damaged when it is extracted from the apparatus for sheet replenishment.